A number of supplemental or auxiliary door locks have been devised for attachment to a hinged door to secure it in a closed position against unauthorized opening. Many of these door locks are not truly portable, because they require that modifications be made to the door jamb or frame. However, several require no such modifications, and may be carried from place to place by the user. Among these are the adjustable brace-type locks that are designed to be placed with one end against the floor and the other against the door, frequently at the doorknob. These braces are generally too large to be carried in a pocket, briefcase or purse, and consequently, smaller and more easily-transported door-locking devices have also been developed. Most of these small, portable door-locking devices are adapted to operate in connection with the type of door having a jamb against which the door abuts when it is in its closed position. Furthermore, many of these locks are useful only with doors having locking bolts that are received in a bolt keeper recess or hole in the door jamb. Thus, for example, U.S. Pat. No. 3,596,961 of Lippman describes a portable door lock having a toothed latch bar with a hook for engaging the side of the keeper hole in a striker plate on the door frame. A resilient U-shaped band is provided that is slidable on the latch bar, and which has overlying cross tabs extending across the ends of the "U" to engage the teeth and thereby to block the door from opening.
U.S. Pat. No. 4,589,692 of Boyd describes a portable door lock that includes a thin sheet metal strap that fits between the door and the door jamb. This strap has a fixed bolt on one end that is received in the keeper hole of the striker on the jamb when the door is open. The strap is placed with the bolt in the keeper hole, and the door is closed. A locking dog or brace that is pivotally mounted on the other end of the strap is then pivoted so as to overlap the strap and engage against the inner side of the door.
U.S. Pat. No. 5,280,977 of Piva describes a portable door lock that includes a generally flat base having a tooth thereon that is adapted to be received in the keeper hole of the striker on the jamb when the base is positioned next to the jamb and extending into the room to be locked. A locking arm connected to the base is movable against a bias inherent in the arm to a position that blocks the door from being opened. A peg may be inserted between the locking arm and the base to hold the arm in the blocking position against the bias.
U.S. Pat. No. 5,415,444 of Hull et al. describes a portable door lock that does not require cooperation with a keeper hole in a door jamb. However, this door lock does require cooperation with a door knob. This lock includes a metal or plastic flexible strap that is attached at one end to a pair of interlocked tubular bars. The tubular bars are positioned outside the door at the base thereof with the strap passing underneath the bottom of the door. The other end of the strap has a bolt through it which is encircled by a loop of one end of a rope or cable. The other end of the rope is formed into a second loop that encircles the doorknob. In use the tubular bars are positioned so that one of the tubular bars abuts the outside of the door and the other abuts the outside of the adjacent door frame. The rope is then tightened to pull the strap taut so that the door cannot be opened from the outside.
U.S. Pat. No. 1,607,789 of Baker describes a portable door lock that is not designed for operation on doors that cooperate in closing with a door jamb. This lock comprises a U-shaped frame having a plurality of leaves therein. The leaves are pivotally connected to each other and to the frame by a pivot pin. The pivot pin extends through slots in the side walls of the frame thereby permitting the frame to be adjusted relative to the leaves. The forward ends of the outside leaves on each side are provided with right-angularly bent, laterally-directed biting teeth for engaging a door and a cooperating door frame when the leaves are positioned in the space or gap therebetween. In addition, each leaf is provided with a plurality of equidistantly spaced teeth that are aligned with each other. The frame also includes a bifurcated foot that is adapted to engage between the teeth on the leaves and to abut with the door and frame when the lock is in place on the door. By providing a plurality of leaves in the frame, the lock of Baker can accommodate a variety of gap sizes between the door and its cooperating frame. However, the lock of Baker is somewhat complicated in that it includes many cooperating parts.
Another portable door lock which does not require that a door abut against a door jamb in its closed position is that of U.S. Pat. No. 4,326,394 of Stein. However, this door lock, unlike the others described herein, is designed for locking a door from the outside only. It includes a metal Z-shaped bar which is adapted for insertion between a door and a door frame. Both parallel sides of the Z-shaped bar are provided with a series of holes, and the lock assembly also includes a front and a rear sliding bar, each having a slot that is adapted for receiving the front or the rear portion of the Z-shaped bar. The Z-bar is fitted into the slot of the rear sliding bar, and a bolt is placed through a hole in the Z-bar to hold the rear bar in place so that the transverse arm of the Z-bar engages the front of the door when the door is closed with the Z-bar in the gap between the door and the frame and the rear sliding bar engaging both the frame and the door on the inside of the room to be locked. The slot of the front sliding bar is then placed over the end of the Z-bar outside the room and slid to engage the front of the door and frame. A padlock is then placed through a hole in the end of the Z-bar outside the room to hold the front sliding bar in place.
It can be appreciated therefore that most of the various portable door locks that are known for use in securing hinged doors are designed for use with the standard door and frame arrangement, whereby a hinged door cooperates with a door frame or jamb against which the door abuts when it is in its closed position. Many of the known portable door locks also require that the door have a locking bolt that is received in a bolt keeper recess or hole in a cooperating door jamb. Several of the known portable door locks are somewhat complicated, in that they involve a large number of cooperating components, or they require that the door, frame or jamb be modified to accommodate their use. Consequently, as can be seen from the foregoing discussion, although a number of portable devices have been developed for use in securing hinged doors in the closed position, all are subject to various limitations and disadvantages.